The present invention relates to lubricant compositions and, more specifically, to polyalkylene glycol based anhydrous food grade lubricant compositions. The food grade lubricant compositions of the present invention are particularly useful as hydraulic oils, gear oils, and compressor oils for equipment used in the food processing and packaging industry.
The food grade lubricants are considered to be “indirect food additives” used in equipment in food processing and packaging plants where the lubricant compositions may accidentally get in contact with the food being processed. Food grade lubricants are specially blended compositions comprising base fluids and functional additives in the past cleared by the U.S. Food and Drug Administration (FDA) and approved by U.S. Department of Agriculture (USDA) as H-1 lubricants. The H-1 lubricants were regulated in 21 C.F.R. §178 (at 178.3570), 21 C.F.R. §1.72 and 21 C.F.R. §1.82. Today, the lubricant manufacturers and food and beverage processors are themselves responsible to use only lubricants that are generally recognized as safe for use in equipment used for producing, manufacturing, packing, processing, preparing, treating, transporting or holding food since the FDA and USDA are no longer responsible for the assessment and registration of food grade lubricants.
In addition to meeting the food safety requirements, the food grade lubricant compositions must also be effective lubricants. They should lubricate food processing and packaging equipment parts, resist viscosity change, resist oxidation, protect against rust and corrosion, and provide wear protection. The lubricating compositions should also perform effectively under various lubrication conditions ranging from hydrodynamic thick film conditions to boundary thin film conditions.
In general, the food grade lubricant compositions are formulated from at least one base fluid and at least one food grade functional additive employed for its known use. The base fluid can be either a mineral oil or a blend of mineral oils, or a synthetic fluid. Medicinal white oil, corn oil, palm oil, and cottonseed oil are some of the mineral oils that are known to be suitable for use in food grade lubricants. Polyalphaolefins (PAO), polyalkylene glycols (PAG), and polyethylene glycols (PEG) are synthetic fluids that are known to be suitable for use in food grade lubricants. The synthetic fluids offer superior oil life, load carrying and anti-wear performance and perform well at high and low temperatures. Various known functional additives that are generally recognized as safe for use in food grade lubricants may be added to the base fluid for their known uses.
Polyalkylene glycols (PAG's) are widely used in the lubricants industry as a base fluid or as an additive in compositions. The predominant chemistries used are random copolymers of ethylene oxide (EO) and propylene oxide (PO), and also homo-polymers of propylene oxide.
The 21 C.F.R. §178.3570 regulation allows for polyalkylene glycols (PAG's) of medium and high viscosity to be used for food grade lubricant applications. That is, PAG's having molecular weight greater than 1500 can be used. PAG's with molecular weights greater than 1500 are not useful for lubricant applications requiring low viscosity. The viscosity of a neat EO/PO copolymer of 1500 molecular weight is about 130 cSt at 40° C. The viscosity of a PO monol is typically 120 cSt at 40° C. Both of these are well above the required range of 32 cSt to 100 cSt for many lubricant applications. Low molecular weight PAG's (those having molecular weight less that 1500) cannot be used since they are not recognized by the 21 C.F.R. §178.3570 regulation as being safe for use for food grade lubricant applications. The three specific classes of H-1 acceptable PAG's described in 21 C.F.R. §178.3570 are:
1. [alpha]-Hydro-omega-hydroxypoly(oxyethylene)poly(oxypropylene) produced by random condensation of mixtures of ethylene oxide and propylene oxide containing 25 to 75 percent by weight of ethylene oxide; minimum molecular weight 1,500; (Chemical Abstracts Service Registry No. 9003-11-6.) The minimum viscosity attainable with this type of fluid at 1500 molecular weight is about 130 cSt at 40° C.
Commercial examples of this type of fluid are: Synalox™ 40-D150, or UCON™ 68-H-1400, both available from The Dow Chemical Company.
2. [alpha]-Butyl-omega-hydroxypoly(oxyethylene)poly(oxypropylene) produced by random condensation of a 1:1 mixture by weight of ethylene oxide and propylene oxide with butanol; minimum molecular weight 1,500; (Chemical Abstracts Service Registry No. 9038-95-3.) The minimum viscosity attainable with this type of fluid at 1500 molecular weight is about 125 cSt at 40° C.
A commercial example of this is: UCON 50-HB-660.
3. [alpha]-Butyl-omega hydroxy-poly(oxypropylene); minimum molecular weight 1,500; (Chemical Abstracts Service Registry No. 9003-13-8.) The minimum viscosity attainable with this type of fluid at 1500 molecular weight is about 120 cSt at 40° C.
A commercial example of this is: UCON LB-625.
Low viscosity food grade lubricants can be formulated using polyethylene glycols (PEG's). However, PEG's have a major disadvantage in that they have high pour points. A specific shortcoming of this type of product is the relatively high pour point, (about −9° C.), which can lead to solidification in equipment when the equipment is shut down at low ambient temperatures. When this occurs, the equipment cannot be restarted until the fluid is heated externally. This prevents the use of 100% PEG's as a base fluid for formulating lubricants for many applications. Although PEG's are not listed on the 21 C.F.R. §178.3570 regulation, they are generally recognized as safe for use in food and are listed on 21 C.F.R. 178.3910 regulation.
Various types of synthetic food grade lubricants have been described in the literature and used commercially. Examples include water based food grade lubricants containing polyalkylene glycols (PAG's) having molecular weight greater than 1500, polyethylene glycols (PEG's), or polyalphaolefins (PAO) and various additives.
U.S. Patent Application Publication No. US 2002/0115573 A1 (Hei et al) discloses a food grade aqueous lubricating oil for use in conveyor processing of foods (that is, for lubricating the interface between the surface of a can or bottle food container and the moving conveyor). The lubricants typically comprise edible oil and can also contain a variety of other functional additives. The lubricant can also contain an (EO)x(PO)y(EO)z surfactant block copolymer where EO represents ethylene oxide residue, PO represents a propylene oxide residue, and each x, y and z is an integer of about 2 to about 100.
George B. Kelly and George W. Buttrick, Tappi (1970), 53(10), pp. 1900-1904 disclose that polyethylene glycols, methyl ether of polyethylene glycols and random copolymers of ethylene oxide and propylene oxide are each effective lubricants for paper coatings containing starch and starch-latex binder system.
Polish Patent Nos. 149,256 and 154,393 disclose a fire resistant hydraulic-lubricating fluid comprising diethylene glycol or propylene glycol, an ethylene oxide/propylene oxide polymer, and a major portion of water.
Japanese Patent No. JP 62/121,793 (Daiichi Kogyo Seiyaku Co., Ltd.) discloses a heat-resistant water-based hydraulic fluid containing (a) water, (b) glycerin-ethylene oxide-propylene oxide copolymer (MW=40,000; propylene oxide=60 wt %), and (c) propylene glycol-ethylene oxide-propylene oxide copolymer (MW=600; ethylene oxide=50 wt %).
U.S. Pat. No. 6,087,308 (Butler et al) discloses a food grade lubricating oil which contains a major amount of a food grade natural or synthetic base oil in combination with a minor amounts of food grade additives including a thickener, an antioxidant, a rust inhibitor, an anti-wear additive, an antifoam, and a coupling agent. Synthetic base oils disclosed are food grade polyalphaolefins.
U.S. Pat. No. 5,538,654 (Lawate et al) discloses a food grade lubricant comprising (a) a major amount of a genetically modified vegetable oil or synthetic triglyceride oil, and (b) a minor amount of a performance additive.
U.S. Pat. No. 4,062,785 (Nibert) discloses a non-aqueous food grade lubricant comprising a major amount of a mineral oil and a minor amount of a fatty amide.
New non-aqueous food grade lubricant compositions have now been discovered. These new food grade compositions overcome the disadvantages of the known food grade lubricants. It has now been discovered that the blend of PAG's and PEG's surprisingly provide a lubricant compositions with good lubricity, low viscosity and a pour point of about −22° C., which gives a greatly increased margin of protection. In addition, good biodegradability and low aquatic toxicity of these new food grade lubricant compositions makes them very attractive for use in machinery for food processing and packaging applications where environmental friendliness is important. These new non-aqueous food grade lubricant compositions are water soluble and as such they can be used in any application requiring a water soluble machine lubricant.